In an inverter which supplies power to a motor or in a voltage converter which converts voltage, a structure may be adopted in which a semiconductor element which generates a large amount of heat, such as an IGBT, is integrated separately from other circuits, and is cooled intensively. In one such integrated structure, a semiconductor stacking unit is known in which a flat type semiconductor module for containing a semiconductor element, and a flat type cooler are stacked alternately (e.g., Patent Document 1 to Patent Document 3).
In order to transfer heat well from the semiconductor module to the cooler, the semiconductor stacking unit is placed on a frame while pressure is being applied to the semiconductor stacking unit in a stacking direction. Here, the frame is a structure for supporting the semiconductor module, and typically may be a housing of the electric power converter. In order to apply pressure to the semiconductor module, a spring is fitted between one end surface of the semiconductor module in the stacking direction and a wall or support provided on the frame. A technique for improving the efficiency of an operation for inserting a compressed spring between the wall or support of the frame and the semiconductor module is disclosed in Patent Document 1 to Patent Document 3.
Patent Document 1 discloses a technique in which, after compressing a clip-shaped flat spring, the clip is inserted between a semiconductor module and a wall of a frame. The techniques of Patent Document 2 and Patent Document 3 both employ a spring unit in which a coil spring is sandwiched between two plates. The technique disclosed in Patent Document 2 is as follows. The spring unit is inserted from a slit provided in a wall of a frame, and the spring unit is compressed while its front side plate is pressing against the semiconductor stacking unit. When a rear side plate has passed through the slit, the rear side plate is rotated by 90 degrees. When the pushing force on the rear side plate is released, both ends of the rear side plate engage with both sides of the slit and the spring unit applies pressure to the semiconductor stacking unit, thus fixing the semiconductor stacking unit. The technique of Patent Document 3 is as follows. A bolt is inserted from a rear end plate while the spring unit is in a compressed state, and the bolt is engaged in a screw hole provided in a rear surface of a front side plate. Thus, a spring unit which is held in a compressed state can be obtained. The spring unit which is held in the compressed state is placed between a semiconductor stacking unit and a wall of a frame. A rear side plate of the spring unit is fixed to the frame. Next, the bolt is disengaged. Upon disengagement of the bolt, the spring is released, and the spring unit applies load to the semiconductor stacking unit, fixing the semiconductor stacking unit.